Permanent magnet alloy



Nov. 9, 1954 D. HADFiELD 2,694,166

' PERMANENT MAGNET ALLOY Filed July 10, 1951 2 sheets-sheet 1 (BH) max. t d gouss-oers e HG L 600 700 H BOO 9OO oersted Inventor B m M Attorney NOV. 9, 1954 HADFlELD 2,694,166

PERMANENT MAGNET ALLOY Filed July 10, 1951 2 Sheets-Sheet 2 Hc oersted FIG. 2.

BOO

650 l 2 3 4 /0 (8H) mox. Cb gousssted 6' O x FIG. 3.

3.5 l 2 3 4 Ihventor Bywm d-fi a, a mam Attorney United States Patent 2,694,166 PERMANENT MAGNET ALLOY Dennis Hadlield, Shellield, England, assignor to William 2,694,166 Patented Nov. 9, 1954 Fe-Ni-Al-Co-Cu type containing about 12.5% to 14.5% nickel, 7.5% to 8.5% aluminum, 23.5% to 25.5% cobalt, 2.9% to 3.3% copper, less than 0.05% carbon, and columbium within the range of 0.5% to 3.25% (all with- Jessop & Sells Llmlted, Shelfield, England 5 in the usual manufacturing tolerances), with the balance Application July 10, 1951, Serial No. 236,052 mainly iron, said magnet having in a preferred direction a 9 Cl i ((31, 317.402 coercivity of at least 630 oersted increasing approximately linearly with the amount of columbium selected from the This nvention relates to permanen -mag e a y Q said range and a (BH)max. in gauss-oersted in accordance the Alhleh typ -A t0 Whleh m qp 10 with the approximate mutual relationship, valid for characteristics have been imparted, and 1s a contmuatlon- 131 1 mm fat1 a t3 8 106, m-part of U. S. patent application Serial No. 59,183, filed 3 2 November 9, 1948, now abandoned. -Q

The method of P e P Permanent where P is at least 4.9 and Q has a maximum of 400. t as how largely Praetlsed has Its basls 111 Work. y It is a result of the stated relationship between coe ahd l W S Y as t y Set out In a letter ercivity and (BH)max. that the latter decreases as the Published lll'the 158116 of Nature dated y 30, 19.38 former is increased, but the combination of the two (P- Suhletfted a Permanent magnet alloy of h Alhlco properties in any magnet having its columbium selected YPe the aetloll of a maghetle field Whllst eoollhg from from the range 0.5% to 3.25% always has high values for hlgh temperature Sheh e mp 12000 both properties, and in general includes coercivity ma- Slhee that date, such treatment has been BPl a terially, or even substantially in excess of 650 oersted. large scale to m g alloys capable f attalfl1hg Thus at the minimum value of coercivity of 630 oersted P e 'l and, althohgh valjlous addltloh$ obtainable with columbium selected from about the botnotably of tltanlum -to the basic Fe-Nr-Al-Co-Cu alloy tom f h range, the corresponding (BH)max. is in have been proposed in endeavours to achieve still better excess f 4 75 10s gaussoersted i h h d t magnetw p p pr e forsome y r p been HcX(BH)max, at least 308x10 with a coercivity of largely eohfihed t0 thls basle Y, It pp that about 700 oersted obtained with columbium approaching that alloy yielded the best results in the present state of 1% h (BI-1) i i x e of 4.50 10 gauss-oersted knowledge; and may approach 5.50 10 gauss-oersted, H 0X max.

Even P t0 the p ll 0f the Work y OllVer a being at least 3.15 X10 Again with a coercivity of about Shedden. nu r adghtlons h d been p p to Alqlco 750 oersteds, the BH)m-..X. still has the high value of at alloys to improve their properties (then, of course, 1so- 1 425 106 gauss-oersted (H (BH) ,=318 10 p P t0 laelhtate their manufacture; d, Sin e and does not fall below 4.00 10 gauss-oersted with inthe Present lhvehtleh 15 based the dlSeOVel'Y that Very crease of coercivity to about 800 oersted or even higher advantageous results may be achieved with anisotropic al- (HcX (BH)max. at least 320x10 Magnets are obl y 0f the type in gues y the addltlon 0f eolumhlum tainable according to the invention with coercivity of at in amounts lying within a well-defined range, it is relevant least 825 oersteds d a accompanying (BH)max. of to mention that British patent specification No. 496,774 415 to 4 5 1() gariss-oersteds (H (BH) at least (dated November 5, 1937, and accepted December 6, 3 5 1 )9) 1936) described the addition of columbium to an isotropic 40 Th remanence f. th magnets is likewise high; as is {3111160 Permanent magnet alloy e h P p of necessary with (BH)max. values of the order previously lng the harmful effects of contammatlon by carbon to the lifi d,

magnetlc PTOPeFtIeS 0f the Y- Various examples will now be given of different com- Smce 1937, the general adoption of mductlon furnaces iti of ll th thermo-magnetic, thermal, and for h t magnet alloys has mlleh l'edlleed carbon e magnetic treatments used with them, and the resultant tamlhatloh, 9 t Q- ealhoh WOUlQI'ahk as hlgh magnetic properties in the preferred direction. All the amount of l'hlS impurity; 0.02% to 0.03% is the maximum ll were prepared as castings now found in the best commercial alloys. It is, therefore, T castings were prepared ith th following h k l lg tgcgg i e g e pi s s i sflallef tg 0f t f has ta y analyses (which incllicate the kind of departure that may e ng e ec on e magne 1c proper les, r t but British specification No. 496,774 shows that as little as be expected f om t e 5 32 2 round figure analysls) 0.2% to 0.3% columbium would be ample to neutralise it.

As indicated above, the present invention makes use of a definite amount of columbium in anisotropic permac N0 Cu, nent magnet alloys of the Fe-Ni-Al-Co-Cu type, and the cent cent cent centcent object of the invention is to obtain permanent magnets of this type having a high coercive force in the preferred 1330 2M0 direction, and particularly having a combination of high 13'62 24'72 coercive force and high (BH)max. better than has hitherto h been obtainable in magnets of such high coercivity. h balance being iron and the ustlal eafhoh (less than When a permanent magnet alloy is mentioned in the and impuritiespresent specification, it is to be understood that this s P s Were P p all being of the same Size, term applies alike to a casting produced by melting the X 10 -l and all heated to a high Solution teth' constituent elements together and to a sintered mass properature of 1250 C. and then Co l d in a maghetie field duced by subjecting a powdered mixture of those elements directed along their 40 mm. dimension at an average rate to pressure in a mould and heating the compact, it having a of 1.5 C. per second down to 600 C. according to the been found that such a sintered mass behaves very similarnow well understood practice for producing anisotropic ly to a casting of like composition when both have been magnets. The test pieces were then subjected to the subjected to similar thermo-magnetic, thermal, and mag usual kind of ageing process in which they were tempered netic treatments required to achieve anisotropic characfor one hour at 680 C. and furnace cooled to 400 C. t i ti over a period of 22 hours, followed by further ageing According to the present invention, a magnetically at 560 C. for 16 hours. The pieces were ground on anisotropic permanent magnet consists of an alloy of the their contact ends only. The magnetic properties were:

Table II Rema' coercivity (BEDEM' Ho Ref. CastNo. Coohng r 223:: oersted g gg (Brow. No-

1 1.5 C.lsec... 12,200 658 4.78X10 314x10 1 2 ..do 10,950 752 425x10 319x10 2 The test pieces were then re-tested after being ground on all faces as is necessary'to obtain a really'true comparison between test pieces. These gave re-tested, the following characteristics, showing a slight improvement:

Further" castings were also prepared with thefollowing compositionsgenerally resembling that of Cast No. 2

(Table I), but with rather more columbian:

Table VII All further test p1eces referred to below were ground 20 on all faces. 05

st N1, Per- Al, Per- 00, Per- 011, Per-- Ob, Per- Fe eta, Further samples of Cast No. 2 were cooled from the N0. cent cent cent cent cent Percent solution temperature at C./ sec. and 0.5 C./ sec. respectively, but otherwise treated exactly as before, when 52 156 24.96 314 2498 Ba1ancc the following characteristics were obtained: 13. 52 7. 74 25.20 3.30 2.81 D0. 13.36 7. 48 25.08 3. 12 2. 94 Do. 13. 44 7. 5s 25. 08 3. so 2. 80 D0.

Table IV Rema- (BEDMX. Coercivity HcX Ref. Casi; N0. Cooling rate nence gaussgauss oersted casted (BEDMX. No..

2 1.0'O./sec 10, 900 784 4.04-. 10 3.15 10 5- 2 0.5 C./sec 10,940 785 405x10 3.16 10 6 This indicates that a slower cooling rate than 1.5 C./sec. improves coercivity, at the expense of some reduction in (BH)max. but that there is negligible difference between cooling rates of 1.0" C./sec. and 05 C./sec. Atany of the variations in cooling rate that are known to be acceptable, the magnet alloys according to the invention have characteristics superior to any shown in the prior art.

Further castings were prepared with the following compositionsgenerally resembling that of Cast No. 1 (Table I), but with rather less columbium and with the cobalt including value approximately 1% above and below the general average of 24.5%:

Table V Ni Per- A1 Per- 00 Per- Cu Per- Ob Per- Gast dent dent eent. cbnt dent 13. l i 8.04 23. 7G 3. l0 0. 70 12. 5 I 8. 25. 3. 18 0. 74 13. 0S 8. 1 24. 36 3. 2 0. 72 13. 12 I 8. 06 24. 24 3. 17 Q 0. 65

the balance being iron and impurities.

Test pieces, of the same size as before, were heated to a solution temperature of 1250 C., cooled at 1.4 C./ sec. in a magnetic field to 600 C., and subjected to an ageing process: 590 C. for 32 hours, followed by 560 C. for

the usual carbon and Cooling from a solution temperature of 1250 C. was at 06 C./sec. andthe ageing process was 595 C. for 48 hours, followed by 560 C- for 48 hours. were ground all over, magnetized, and tested. The mag: netic properties were:

Further castings were also prepared with the basic composition:

Table IX Ni, Al, Cu, 011, Gb, Fe etc Percent Percent Percent Percent Percent 13. 5 8. 0 24. 5 3.0 0. 7 Balance.

Each cast was cooled from a solution temperature of 1250 C. at a rate of 1.4 C./sec. and then sub ected to alternative two-stage ageing treatments:

A. 590 C. for 32 hours followed by 560 C. for 32 hours B. 640 C. for 2 hours followed by 560 C. for 16 hours The pieces.

The magnetic properties were:

Table X Ageing Treatment A B Cast No.

B H )max- Ref H (BH)m-x- Ref fis oerst ed gig No. E5533 oerstied $235 No.

670 5 20 10 12, 550 680 681 5 X10 12,270 680 668 10 10 12,500 676 675 5 16x10 12,250 679 684 5 01x10 12,050 690 684 5 00x10 12,250 680 083 5 o5 10 12.320 684 682 5 24 1m 12,350 078 681 496X10 15 12,300 690 570 5 11x10 12,540 658 further above that line. They have the approximate A B 25 equations. Line cd:

Average H., (BH)..,.x 3,45X10i 3.48X10 H)max-=( X 35 .'6 (2) Line ef: Further castings were also prepared in the samecast B 57 106 H 3 2 3 with the basic composition as in Table IX, one being H)mx X c subjected to cooling slowly from a high solution temperature, with long two-stage ageing, and another to slower cooling from a low solution temperature, with shorter three-stage ageing:

Table XI I Solution 3:? Tgnp Cooling Rate Ageing 40 21 1,250 1.4 0./sec. 590 0. for 32 hours and 560 C. for 32 hours. 21 950 0.5 C.lsec 590 C. for 9 hours, 560 0. for 15 hours, and 520 G. for 24l1ours.

The magnetic properties were:

Figure 1 of the accompanying drawings 'shows'graphically the field in which (BH)max, is plotted against coercivity (He) for most of the results cited above as Reference Nos. 1 to 20. In the case of Table X, (which shows the substantial consistency of properties attainable by the invention in ten pairs of casts), only four of the twenty sets of results have been selected for inclusion in Figure 1. The plots are correspondingly identified as 1 20 in Figure l, and it will be seen that all lie on a line a b or to the upper right hand side of that line, i. e., in an area (shown heavily shaded) in which both He and (BI-Durex. tend to increase above the combination of those values represented by points on the line ab itself.

The a b (not quite an arc of a circle) is represented by the equation as may be checked from the following values of (BH)max. calculated from the equation:

700 750 800 oersted. 4.50 4.17 3.78X10 gauss-oersted. 3.15 3.13 302x10 t Line ef completes with lines ab an area in which lie the above cited results of magnets according to the invention (i. e. with He of 650 oersted or substantially more), and line at represents an approximate mean across the area between the lines ab and e7. In the area, any movement in the direction of the arrow, i. e., approximately normal to these three lines, shows simultaneous increase of H5 and (BH)max.

It follows that a movement in the opposite direction shows a simultaneous decrease of H5 and (BH)max.Z and, when the line ab has been crossed in this reverse direction, some substantial distance has to be covered before the line hk is reached. This line forms the boundary of an area (shown lightly shaded) in which lie corresponding values of Ho and (BH)max. of anisotropic permanent magnets of the Alnico type heretofore known, none of these having any content of columbium. There being the distinct gap between the two areas, it is evident that no magnet belonging to the lightly shaded area and having any particular value of He can have a value of (BH)max. as high as a magnet having that same value of H5 and belonging to the heavily shaded area, i. e., in the area relating to the present invention. And likewise no magnet belonging to the lightly shaded area and having any particular value of (BH)max. can have a value of He as high as a magnet in the heavily shaded area. i

The lower limit of columbium according to the invention is 0.5%, which is the approximate minimum quantity necessary to achieve Ho of at least 650 oersted (note the line ace), with accompanying high (BH)max.at least 4.75 10 gauss-o'ersted. As a check, the point 21 is shown in Figure 1, representing Hc of 630 oersted and (BH)max. of 4.86 10 gauss-oersted obtained with a cast substantially identical with Casts Nos. 1 and 2 (Table I) but with columbium of 0.49%.

The point 22 is also shown in Figure 1, representing H5 of 751 oersted and (BH)max. of only 2.7 1O gaussoersted obtained with a further similar cast, but with columbium'of 5.3%. the line ab through a point g, corresponding to the curving back through the point I known to exist in the continuation of the line hk bounding the lightly shaded area. The upper limit of 3.25% columbium according to the invention produces magnets with He and (BH)max. plots lying beyond the line ab before it begins to.curve back, i. e., before both Ho and (BH)max. de crease simultaneously.

It will be noted that He tends to increase with in-- This indicates a curving back of bered to correspond with the points in the heavily shaded area of Figure 1. They lie in an area, an indication of some departure from a truly linear increase of He with columbium content within the stated range. A spread of this kind is to be expected with minor variations found in check analyses from the intended round-figure" analysis, and with variations in the thermo-rnagnetic, thermal, and magnetic treatments of which indications have been given above.

Figure 3 shows a similar plot of (BH)maX against. columbium content, with a similar spread" evident:

Apart from the interdependence of He and (BH)-max. as shown by Equations 1, 2 and 3, the products of; He and (BH)max. given above also demonstrate that the. combination of lie and (BH)ma. values remains hi h a decrease in (BH)max. being compensated by an crease in He. The products at intervals along the line; a b have been shown to be in excess of 3.0 and it will be evident that all the points 1 to plotted'have. products in excess of 3.0 10 Points on the line as", e. g. 15, 18, have products in excess of 3.4 10 and points nearer the line ef, e. g. 10, '7, 12, 13, have prod ucts: about 3.7 X10 or even greater Columbium is rarely, if ever, obtainable on a com.- mercial scale free from tantalum, as the separation. of the two is diflicult. The references to columbiu-rnin this specification are to be regarded as including a proportion of tantalum fortuitously present with the columbium. But tantalum alone is incapable of achieving the high combination of H and (BH)mzx. values that the invention shows to be possible with columbium. Any content of tantalum with columbium shouldtherefore be limited. Anisotropic permanent magnet alloys containing material quantities of tantalum in addition to columbium are described and claimed in corpending U. S. patent application Serial No. 236,053 of even date herewith, likewise a continuation-in-part of U. S; patent application Serial No. 59,183.

The columbium is most convenientlyv introduced in the form of ferro-columbium, the iron content of which l'IHlSi. be allowed for in the ultimate composition of the any.

Cooling rates of 1.5, 1.0, and 05 C./sec. have been mentioned above, and it will be seen that the magnetic properties are not largely influenced by changes in this rate. The alloy not being unduly sensitive in this direction, a wider range of cooling rate than this available, say from 0.2 C./sec. to 5 C./sec.

Generally, the slower the cooling rate the higher the. coercivity but the lower the remanence and (BH)ma.\;. whilst the faster the cooling the higher the remanence and (-BH)max. but the lower the value of the coercivity. Consequently it is desirable to use the slower cooling rates for very short magnets and to increase the rate for longer magnets.

Further, it is generally advisable to reduce the coolingrate when the nickel content is reduced and to increase it when the aluminum content is reduced and vice versa.

For the purposes of the present invention, carbon,

chromium, manganese, molybdenum, phosphorous, and

silicon, silver, sulphur, titanium, tungsten, vanadium, or zirconium, are regarded as impurities (included, if present, with the balance of Fe etc. and should not be present in amounts exceeding a total of 1%. Carbon should be (and is, if induction heating is used) kept lowbelow 0.05%.

What I claim is:

1. A magnetically anisotropic permanent magnet consistin of an alloy of the Fe-Ni-Al-Co-Cu tyne containing about 13.5% nickel, 8% aluminum, 24.5% cobalt, 3% copper (within the usual manufacturing tolerances) less than .05% carbon, and 0.5 to 3.25% columbium, with the balance mainly iron, said magnet having in a preferred direction a coercivity in the range 630 to at least 780 oersted, a remanence in the range 10,000 to 12,250 gauss, and a (BH)ma.x. in the range, 4.04 to 4.86 10 gauss-oersted, the -product of the coercivity and the (BH)max. of the magnet being between about 3.0 10 and 3.2 10

2. A magnetically anisotropic permanent magnet consisting of an alloy of the Fe-Ni-Al-Co-Cu type containing about 13.5% nicke1-, 8,r%..aluminum, ;24.5,% cobalt, 3% copper (within the usual manufacturing tolerances) less than .05% carbon, and 0.5% to 1.0% columbium, with the balance mainly iron, said magnet having in a preferred direction.- a coercivity in the range 630 to 670 oersted, a remanence of about 12,250. g'auss, and a (-BH)max. in the range 4.25 to 4.86 10 gauss-oersted, the product of the coercivity and the (BH)m8.X. of the magnet being between about 3.1 10 and 3.2 l0

3.. A magnetically anisotropic permanent magnet con sisting' of an alloy of the; Fe-Ni-Al-Co-Cu type containing about 13.5% nickel, 8% aluminum, 24.5% cobalt, 3% copper (Within the. usual manufacturing tolerances) less; than- .05% carbon, and 1.0 to 3.25% columbium,

- with the balance mainly iron, said magnet having a. preferred direction a coercivity in the range 670 to at, least 780 oersted, a remanence in the range 10,000. to; 12,000, andsa (BH)m a .x. in the range 4.04 to 425x10 gauss-oersted, the product of the coercivity and the s, (BH)max-; of the magnetbeing betweengabout 31x10 and 3.2 10

4. A magnetically anisotropic permanent magnet consisting of an alloy of the Fe-Ni-Al-Co-Cu type containing about 13.5% nickel, 8% aluminum, 24.5% cobalt, 3% copper (within the usual manufacturing tolerances) less than .05 carbon, and about 3.7 columbium, with the balance mainly iron, said magnet having in a prefer-reddirection a coercivity in the range 750 to at least 780 oersted,. a remanence of about 11,000 gauss, and (BH)max. in excess of 4.0) l0 gauss-oersted.

5. A magnetically anisotropic permanent magnet, con? sisting of an alloy of the Fe-Ni-Al-Co-Cu type containing about 13.5% nickel, 8% aluminum, 24.5% cobalt,

1 3% copper, less than 0.05% carbon, and about 0.8 c01um-.

bium (all within the usual manufacturing tolerances) with the balance mainly iron, said magnet having in a preferred direction a coercivity in the range 650 to 700 oersted, and (BH)IK18.X. in excess of 4.5 X10 gauss-oersted.

6. A magnetically anisotropic permanent magnet, consisting of an alloy of the Fe-Ni-Al-Co-Cu type containingabout 13.5 nickel, 8% aluminum, 24.5% cobalt, 3% copper, less than 0.05% carbon, and 0.5% to 3.25

columbium (all within the usual manufacturing tolerances), with the balance mainly iron, said magnet having in a preferred direction a coercivity of between 630 and 840 oersted, a remanence of about 10,000 to 12,000 gauss, a (BH)max, of between 3.8XlO and 5.5 -10 gauss-oersted, the product of the coercivity and the (BH)max. of the magnet being between 3.0)(10 and 3.8 ;10 t

7. A magnetically anisotropic permanent magnet, consisting of an alloy of the Fe-Ni-Al-Co-Cu type containing about 12.5 to 14.5% nickel, 7.5% to 8.5% aluminum, 23.5% to 25.5% cobalt, 2.9% to 3.3% copper, less than 0.05% carbon, and columbium within the range.

0.5% to 3.25% (all within the usual manufacturing tolerances), with the balance mainly iron, said magnet having in preferred direction a coercivity in the range aso t ab ut 50 e and a (BH)max. in the range 3.8 10 to about 5.5 X10 gauss-oersted, the product of the coercivity and the (BH)max. of the magnet beingbetween about 3.0)(10 and 3.8X10

8. A magnetically anisotropic permanent magnet consisting of an alloy of the Fe-Ni-Al-Co-Cu type containingabout 13.5% nickel. 8% aluminum. 24.5% cobalt, 3% copper, less than .05 carbon, and 0.5 to 3.25% columbium. with the b lance substantially all iron.

9. A magnetically anisotropic magnet consisting of an alloy of the Fe-Ni-Al-Co-Cutype containing about 13.5 nickel, 8% aluminum. 24.5% cobalt, 3% copper, and 0.5 to 3.25% columbium, with the balance substantially all iron.

References Cited in the file of this patent FOREIGN PATENTS Number Country Date 496,774 Great Britain Dec. 6, 1938 522,731 Great Britain June 26, 1940 

9. A MAGNETICALLY ANISOTROPIC MAGNET CONSISTING OF AN ALLOY OF THE FE-NI-AL-CO-CU-TYPE CONTAINING ABOUT 13.5% 0.5 TO 3.25% COLUMNIUM, WITH THE BALANCE SUBSTANTIALLY ALL IRON. 